The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Lighting, whether indoor or outdoor facilities, is one of the largest energy consumers in developed countries and is typically extremely inefficient. The U.S. Energy Information Administration (ETA) estimates that in 2010 about 499 billion kilowatt-hours (kWh) of electricity were used for lighting by the residential and commercial sectors. This was equal to about 18% of the total electricity consumed by both of those sectors and about 13% of total U.S. electricity consumption. The efficiency of lighting varies by the particular type of lighting technology. Incandescent lighting is approximately 10% efficient, fluorescent lighting is approximately 50% efficient, and light-emitting diode (LED) lighting is approximately 80% efficient. These energy losses are generally attributable to heat generation. Thus, for an incandescent light, nearly 90% of the energy used is lost in the form of heat while only 10% of the energy is converted to light. A 100 watt light will produce 90 watts of heat. Heat in turn can cause a secondary effect on efficiency through the additional need for air conditioning.
Significant efforts are being made to reduce these energy losses. For example, incandescent lamps are being phased out by federal law. The most common form of lighting for commercial and industrial uses is the fluorescent lamp. All fluorescent lights require a ballast circuit to provide the necessary electric energy to “start” the light and keep it running. The visible light produced by a fluorescent light is a 2 step process. First, the mercury in the light must be ionized to produce photons. This is the first step in lighting a fluorescent light. But the high energy photons produced from the mercury ionization is not in the visible spectrum. These photons are converted to visible light when they strike the phosphor material coated on the inner surface of the light which in turn emits photons in the visible spectrum. Once the mercury has ionized, the light can be run in a lower energy state. It is the function of the ballast circuit to control these two steps. Depending on the ballast type, it may also need to be able to detect whether there is a functioning fluorescent light present.
Early ballasts, referred to as magnetic ballasts, consisted of a magnetic circuit that used a starter circuit to initialize mercury ionization. However, this type of ballast is inefficient and in 2010 federal law prohibited the sale of or installation of magnetic ballasts. A new more efficient ballast design emerged in the 1990s: the electronic ballast. It was able to improve efficiency by operating at significantly higher frequencies (50 kHz verses the 50-60 Hz of magnetic ballasts). Electronic ballasts are the type currently in use and, although they increase the efficiency of fluorescent lights by 15%-20% (http://ateam.lbl.gov/DesignGuide/DGHtm/electronicvs.magneticballasts.htm), fluorescent lamps still are not nearly as efficient as LED lights. LED lights can be arranged to fit into devices or housings that have the same form factor as fluorescent lights, but, since LED lights require direct current instead of alternating current, LED lights cannot directly replace fluorescent bulbs without first converting and modifying an AC signal from a ballast.
Efforts have been made to develop devices to replace fluorescent lights with LED lights. For example, U.S. Patent Application No. 2010/0148673 to Stewart et al. teaches an LED lighting device that connects to an existing G23-type fluorescent lighting connector. In Stewart, AC power is converted to DC power, which is supplied to a pulse width modulation (PWM) controller to generate a signal pulse. The signal pulse creates the drive voltage for LEDs. Pulse-width modulation is necessary in the Stewart et al. application to regulate current sent to the LED array. Stewart et al. further discloses that the current through the LEDs is controlled by an LED current controller. A comparator detects voltage drops as current flow through the LEDs, and provides feedback to the LED current controller, thus enabling regulation of power to the LEDs. This system fails to appreciate the advantage of receiving input from different types of ballast, and it also fails to appreciate that voltage and current can be effectively regulated without the use of pulse-width modulation with feedback control.
U.S. Pat. No. 8,330,381 to Langovsky teaches a system of driving an LED array using an output from ballasts typically used to power fluorescent bulbs. To power the LED array this system incorporates, among other things, a pulse-width modulator and a current sensor. However, this system fails to appreciate that an LED driving circuit created without a pulse-width modulator or current sensor can produce desirable results while being made far less expensively. In addition, the current sensor of Langovsky is used to provide feedback to the pulse-width modulator such that the pulse-width modulator can control the amount of current sent to the LED array. Ultimately, Langovsky fails to appreciate the advantages of a system that uses only passive components without implementing any kind of feedback loop to regulate current sent to the LEDs.
U.S. Patent Application No. 2012/0068604 Hasnain et al. teaches a system of powering LEDs that are adapted to fit into existing fluorescent tube lighting sockets. To convert AC signal from a ballast to a DC signal useable by an LED array, the system has implemented a power adapter where the power adapter used in the system depends on what type of ballast it is to be used with. This system fails to appreciate advantages associated with a system that can seamlessly receive input from more than one type of ballast without needing a customized power adapter for each.
U.S. Pat. No. 8,115,411 to Shan teaches an LED lighting system having a voltage feedback constant current power supply circuitry and high power LEDs. Systems of Shan use a pulse-width modulator to control DC current supplied to the LEDs. A voltage sensor receives information from the LEDs and provides feedback to the current control circuit, which can change the current supply to the LEDs via the PWM. Shan, however, requires removal or bypassing of any ballast that may be in place in the existing fixture. As a result, Shan fails to contemplate a system that is compatible with at least two different types of ballasts.
In addition to the above-described patent documents, the following also make efforst to provide solutions to the same issue of replacing a fluorescent light with an LED light: U.S. Patent Application No. 2010/0033095 to Sadwick, U.S. Pat. No. 7,053,557 to Cross et al., U.S. Pat. No. 7,067,992 to Leong et al., U.S. Pat. No. 8,400,081 to Catalano et al. However, none of the references discussed above appreciates that a system for replacing fluorescent lights with LED lights can operate using only passive circuit components, thus creating the need for an improved LED driving lighting device.
All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.